Yes, and I believe you're absolutely correct. Any monopoly will fail to innovate in the absence of any competition in a given market segment.
I would like to add a caveat here...the caveat being that your statement is correct provided the potential TAM itself is not saturated.
Once the TAM has been saturated, sales will drop off as no one needs a new unit - at any price - of the same old tired and old tech.
Intel is sort of in a saturated TAM situation. With or without AMD, if Intel does not innovate to obsolete last year's CPU's then its TAM for upgrades and replacements for next year and the year after will crater.
I'm not talking marketshare, just TAM.
And I think this phenomenon is new to mankind because prior to this generation we did not have the globalization of trade and commerce that we have now, which makes the TAM available upfront nearly all at once.
AT&T and RCA were monopolies but the TAM was restricted to western nations and only the wealthy ones at that, the TAM itself was going to continue to grow though as more and more nations came to be wealthy enough to buy their products even if they were 10yrs old outdated relics.
Intel and the desktop PC is not quite in that same situation. The TAM is already globalized. Intel can't look to tap more countries to expand the TAM. So they really have no choice but to innovate and compete with themselves, unless they want to become a really small company with monopoly high margins, which their shareholders would penalize considerably.